Overview of dendro-archaeological studies in the French Alps: assessing montainous silvicultural practices changes over the last millenium

In the French Alps, dendrochronologists are studying timbers used in mountain (rural buildings, mining structures) for about twenty years. 1730 Larch, Spruce Fir, Scots pine and oaks timbers (cores and sections) were tree ring dated at more than a hundred buildings located between 790 and 2356 m a.s.l. Several felling dates clusters were identified, from the 11th c. to the 20th c. Except during the second half of the 14th century, trees were felled during all times, which testifies to an almost continuous activity of buildings’ maintenance, repairs and transformation. The evolution of felled timbers age and diameter over the last ten centuries reveals the forest resources management by rural societies. We show an increase in the age of the trees felled from the 11th to the beginning of the 14th century, up to ca. 250 years old. From the end of the 14th to the beginning of the 20th century, the trees were felled at a median age of 100 years. Moreover, diameters of the used trees used are more or less constant over time (around 20-25 centimeters), because these dimensions are perfectly suited for the (mostly studied) structural elements of mountain constructions. As diameter has remained constant whereas the age of the felled trees has changed, growth conditions have therefore improved over the ten centuries studied. A climatic explanation is difficult to retain for this medieval-modern period discrepancy. Rather, anthropic explanation, impacting silvicultural practices and favoring growth would be a more relevant hypothesis.